In the treatment of disease, morphological and functional changes that are caused by disease within an organism are important for detecting disease at an early stage. In the treatment of cancer, in particular, learning the position, size, and nature of a tumor early on is extremely important for determining a strategy and protocol. Examples of methods that have conventionally been employed for this purpose, in addition to biopsy by puncture and the like, are image diagnosis by X-ray imaging, MRI, PET, and ultrasound imaging. Biopsy is useful for making a diagnosis, but the burden on the patient is great and it is unsuitable for tracking the progression of lesions over time. X-ray imaging, MRI, and PET necessarily expose the patient to radiation and electromagnetic waves. Further, in conventional imaging diagnosis such as that mentioned above, complex operations and long periods are required for measurement. From the perspective of the size and shape of the device, it is difficult to perform surgery while navigating using these methods during surgical operations.
Fluorescence imaging is an imaging diagnostic method that solves these problems. In this method, a substance that generates fluorescence when exposed to stimulating light of a specific wavelength is employed as an imaging agent. Further, this method comprises the steps of irradiating an excitation beam from outside the organism and detecting the fluorescence that is released by the fluorescent material within the organism.
Cyanine compounds are typical compounds that can be used in the fluorescence imaging method. In practice, indocyanine green (abbreviated as “ICG” hereinafter) is currently employed to test liver function and in ophthalmic angiography. However, ICG dissolves readily, and must be employed in formulations to which iodine is added. There is thus a problem in that it cannot be used in patients who are allergic to iodine.
The compound (denoted as “SF-64” hereinafter) that is described in Claim 1 of Japanese Patent No. 3,507,060, the disclosure of which is expressly incorporated by reference herein in its entirety, is an example of a cyanine compound that solves this solubility problem. This dye is characterized by good solubility in water and low toxicity. It is also described in this patent as having the property of outlining tumors.